1. Field of the Invention
The present invention relates to the application of coatings to high temperature structures, as well as to a method of coating assembled aerodynamic structures so as to provide an impervious barrier at points of assembly to contaminants carried by an environment of high pressure fluid flow.
2. Background of the Invention
The use of high-strength, yet environmentally reactive metals, such as titanium alloys, is well-known in the aerospace industry. It is also well known to use coating compositions to prevent corrosion of these metals resulting from contaminants carried by fluids placed in contact with these metals.
Aerospace vehicles currently being designed for tomorrow's space travel (eg., the NASP vehicle) envision craft capable of ultra-high, indeed hypersonic (Mach 15 and above), velocities. At such speeds, the craft impacts the fluid of its environment with tremendous force. As such, the craft's structures, including points of connection, must withstand not only extreme pressures and temperatures, but also the forced imposition of corrosive environments.
It is therefore imperative that the aerodynamic, fluid-interactive structures and associated joints of these new vehicles be rendered as resistant to corrosive environments as possible. At present, two methods for accomplishing this objective are currently being used.
In the first method, a wet coating material is applied in pre-formed holes of a structure, and a fastener (either threaded or deformable) is inserted into the hole before being secured. However, this method is not desirable because during insertion of the fastener in the hole, the coating rubs off due to contact between the exterior surface of the fastener in the hole interior wall.
In the second method, a structural element is drilled to provide holes, and the element is then coated with a sealing composition. At final assembly, the holes are then reamed. This method has also proven less than desirable because some portion of the holes are left uncoated, and it is impractical to use this two-stage process for major assemblies.